'Bad' Fat Can be Turned into 'Good' Fat, Study Finds

Researchers may have found a way to transform ordinary fat in the human body into a type that burns more energy, based on a new study involving rats.

Switching off a protein in rats' brains turned white fat ? the kind regularly found around our bellies and other places in the body ? into brown fat , a type of fat that burns calories to generate heat. Babies have an abundance of brown fat tissue as a way to fight off cold. Researchers used to think brown fat vanishes as we grow older, but recently found that adults retain some of it.

Boosting a person's stores of brown fat may be a way to fight obesity , the researchers say.

"If we could get the human body to turn 'bad fat' into 'good fat' that burns calories instead of storing them, we could add a serious new tool to tackle the obesity epidemic in the United States," said researcher Dr. Sheng Bi, an associate professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine.

However, much more research is needed before a method could be developed to change white fat to brown fat in people. Researchers want to avoid tinkering with human brains, so an alternative approach would have to be developed.

'Good fat' and 'bad fat'

Bi and his colleagues originally focused their study on a brain protein called neuropeptide Y. This protein is known to regulate appetite. The researchers suspected that inhibiting this protein would cause the rats to eat less.

One group of rats was treated with a virus to inhibit neuropeptide Y. Another group was left alone to serve as a control. After five weeks, the virus-treated group weighed less than the control group, having eaten less.

Then, when both groups were fed a high-fat diet, the virus-treated group gained less weight than the control group.

The results made sense, but the researchers were surprised when they dissected the rats. They found that in some parts of the body of the virus-treated rats, white fat had been replaced with brown fat.

The researchers also found that, when exposing rats to cold for six hours, the virus-treated group generated more heat than the control group.

Fat stem cells

The researchers speculate that inhibiting neuropeptide Y in the rats' brains activated brown fat stem cells stored within the white fat tissue. These stem cells would be precursor cells that could go on to form brown fat.

While brown fat seems to disappear as we age, it could be that brown fat stem cells stick around and simply become inactive.

Injecting brown fat stem cells under the skin of adults might be one way to stimulate weight loss , the researchers say.

The researchers hope to learn more about how signals from the brain cause the white fat to turn into brown fat. If they can identify the molecules responsible for the change, they can perhaps find ways to target the molecules as a new treatment for obesity, Bi said.

The results will be published tomorrow (May 4) in the journal Cell Metabolism.

Rachael Rettner

Rachael has been with Live Science since 2010. She has a masters degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a Bachelor of Science in molecular biology and a Master of Science in biology from the University of California, San Diego.